1. Field of the Invention
The invention relates to a lightweight panel, to its use, as well as to a method for manufacturing the same.
2. Discussion of Background Information
Lightweight panels are used for furniture, doors, walls and the like, because they give the impression of a modern design and high quality at low weight. Thus, the impression of massive shelf units with a width of 5 cm may arise. Starting at a panel thickness of approx. 3 cm, the lightweight panels manufactured according to the state of the art described below have an advantage as regards costs over massive panels, such as chipboard, HDF and MDF panels, for example.
The small specific weight of the lightweight panels reduces the costs for transport and production, makes handling easier during assembly, permits a weaker structural design of the furniture due to their smaller weight, permits the use of fixtures with a weaker structural design because the doors, for example, weigh less, they are cheaper, require lighter, less rugged and, thus, cheaper packaging, and finally is an incentive to buy in the case of self-assembled furniture, because the lighter product can be transported and assembled better by anyone.
Known lightweight panels consist of a light insert whose top and bottom sides are connected to a cover layer. Typical inserts are, e.g., inserts of paper honeycombs or corrugated material, as well as polystyrene foam or rigid PU foam. What is essential with regard to the insert is that the honeycombs protect the two cover layers against compression or stretching and displacement. Paper structures extending in the direction of the thickness, e.g. tubes, honeycombs, triangles, or other structures, which are resistant particularly in the direction of the thickness, are particularly widespread. The cover layers are thin panels, mainly derived timber products, with a thickness of about 3 to 6 mm, whose externally visible surface is either provided with a foil, laminated, printed or varnished for reasons of appearance, or to prevent abrasion or ingress of dirt, moisture and the like. The edges of a lightweight panel may optionally be provided with so-called bars, which mostly are massive. They form the third essential element of a lightweight panel and mainly serve as longitudinal and transversal bars. In the area of the edge, they are fastened between the cover layers instead of the insert, or glued to the edges, they form the edges of the lightweight panel, prevent ingress of foreign substances into the panel, give stability to the edge, contribute to the flexural and twist rigidity of the panel and serve as a fastening for connecting elements, for example for creating a body element from several lightweight panels. In that case, the bars must be integrated into the panels in such a manner that, for example, the forces arising at the corner joint can be absorbed, or that the fastening elements, such as bolt and counter-nut can be sufficiently secured. Suitable materials for bars are usually massive wood, MDF, HDF, chipboards.
Lightweight panels 1 as they are shown, for example, in FIGS. 1 and 2, are manufactured as follows according to the state of the art: the base panel 21 forming the bottom cover layer 2 is placed with the surface 22 that is visible later on facing downwards, and its top surface is provided with glue in its entirety. The longitudinal and transversal bars 41, 42 that have been cut to measure before are laid along the side surfaces of the bottom cover layer 2 onto its pre-glued surface 11. A provisional connection of the longitudinal and transversal bars 41, 42 established before or after this, for example by means of staples 43, in this case provides for an improved dimensional stability and accelerates the working process during the subsequent handling steps. Then, the paper honeycomb panel 3, which has the same height as the bars 4, is laid into the space between the bars. The bottom edge of the honeycombs 3 thus connects to the glued surface 12 of the bottom cover layer. Then, the second cover panel 5 (base 51 and surface 52), whose surface, which is invisible later on, has also been provided with glue before, is laid onto the still-open lightweight panel, such that it can engage in a glued connection with the top side of the bars and honeycombs. Now, the two cover layers of the lightweight panel are pressed against each other while the glue 11, 12 hardens. In order to save time and press capacity, a plurality of lightweight panels are usually stacked one on top of the other and pressed together, and they then harden while being weighted. The manufacture, which takes time and requires a lot of personnel, can be made simpler by using broader bars in the interior, i.e. not in the area of the edges, the bars being laid onto the base panel, for example, in a trussed manner. After hardening, a plurality of smaller lightweight panels are obtained by sawing the large lightweight panel formed thus in the area of the middle of the interior longitudinal and transversal bars.
The method outlined above, which is reminiscent of handicraft techniques, has various disadvantages that prevented their use in mass production until now. Inserting and cutting the bars to size is precision work. Due to the honeycomb structure, a large part of the glue is not used for gluing but hardens unused on the inner sides of the cover layers. The slow hardening process of the glue makes a continuous process impossible because the drying time is several hours. Further problems are the result. For example, commercially available water-based glues, such as, for example, urea glue and PVAC, dry out due to evaporation of moisture. In the process, the paper insert and the cover layer may be weakened. The results is visible unevenness due to deformation of the insert and the cover layer itself. This is the reason why a further step, namely the calibration of the finished, hardened panel is often necessary for obtaining the desired even surface.